docs: def _get_dtype_and_shape(self):
          """
          Get the numpy dtype and shape for image
          """
          npy_dtype = self._get_image_numpy_dtype()
  
          if self._info['ndims'] != 0:
              shape = self._info['dims']
          else:
              raise IOError("no image present in HDU")
  
          return npy_dtype, shape